In air blast circuit breakers, compressed air at a pressure of 20-30 kg/cm2 is employed as an arc quenching medium. Air blast circuit breakers are suitable for operating voltage of 132kV and above. Switching resistors and equalizing capacitors are generally connected across the interrupters. The switching resistors reduce the transient over voltages and helps arc interruption. Capacitors are employed to equalize the voltage across the break. The number of breaks depends on the system voltage (eg: for 132kV 2 to 4 breaks and for 220kV 2 to 6 breaks)
Some of the advantages and disadvantages of air blast circuit breakers are discussed below
Advantages of Air Blast Circuit Breaker:
- Cheapness and free availability of the interrupting medium, chemically stable and inertness of air
- Air blast circuit breakers have advantage of high speed operation
- In air blast circuit breaker fire hazard is eliminated unlike in oil circuit breakers
- Short and consistent arcing time and therefore, less burning of contacts
- Air blast circuit breakers require less maintenance
- They are suitability for frequent operation
- Facility for high speed re-closure
Disadvantages of Air Blast Circuit Breaker:
- An air compressor plant has to be installed and maintained
- In air blast circuit breaker upon arc interruption, the air blast circuit breaker produces a high level of noise when air is discharged to the open atmosphere
- In air blast circuit breaker current chopping problem exists
- There is a problem of re-striking voltage